1. Field of the Invention
The present invention relates to a method and apparatus for analyzing a circuit model by reduction, and a computer program product for analyzing the circuit model, and particularly, to a method and apparatus for efficiently analyzing a circuit model which includes a large number of linear floating resistances, an RC network formed of a grounded capacitance, and a large number of independent current sources, and a computer program product for analyzing the circuit model.
More particularly, the present invention relates to a method and apparatus for analyzing a circuit model by reduction, which can maintain the same level of node voltage in a reduced circuit as a corresponding node voltage of an existing circuit before the reduction, effectively reduce a very large scale circuit with a large number of nodes by using an effective method of reducing a circuit including an RC network and current sources and generating a reduced circuit, and significantly reduce the time required for analyzing the power noise of a chip, which is a significant problem, and the time required for designing a semiconductor chip, and a computer program product for analyzing the circuit model.
2. Description of the Related Art
In recent years, there has been an increased demand for designing very large scale integration (VLSI) circuits having high performance and low power consumption. High performance is achieved by technology scaling, increased functionality, and competitive designs. On the other hand, a common technique used to obtain low-power designs is to scale down supply voltage. This stands to reason, since a chip power P is proportional to the square of supply voltage Vdd. Thus, the demand for high performance and low power consumption has led to modern VLSI designs being characterized by reduced feature size, increased functionality, and lower supply voltage.
Increased chip functionality results in the need for huge power distribution networks. Lower supply voltage, on the other hand, makes the voltage variation across the power distribution network very critical since it may lead to chip failures. In order to provide an ideal supply voltage to each function block in a chip, there must be no loss in a power distribution network. However, an actual power distribution network consists of a lot of small parasitic RC elements, which prevent transferring the ideal voltage value to the function blocks. IR-drop is a voltage fluctuation occurred due to these parasitic RC elements. IR-drop analysis has become an indispensable step for design verification for VLSI design.
IR-drop analysis includes the parasitic RC elements and the function blocks. However, it is impossible to simulate the circuit using a transistor-level simulator due to the non-linear characteristic of the function blocks, which is one of main reasons that make the transistor-level simulation infeasible in most real applications. Thus, the function block is further modeled as independent current sources. However, it is still difficult to analyze the modeled circuit with the transistor-level simulator due to the large size of the circuit. Therefore, it is important to reduce the circuit before analyzing the circuit.
According to a method of analyzing a circuit model by reduction, the size of the circuit is reduced as to lower the complexity of analyzing the circuit. Ideally, the circuit is reduced as small as possible while maintaining the same level of node voltages in the reduced circuit as corresponding node voltages of the circuit before the reduction. Such a method results in a reduced circuit consisting of RC elements with independent current sources.
A power distribution network consists of an RC network with a large number of independent current sources modeled the functional block. Conventional methods of analyzing a circuit model by reduction are used in a circuit only with RC elements. Moreover, a method of selecting a node for controlling an error while reducing the circuit does not exist. Accordingly, a new method of analyzing a circuit model by reduction is required, which can reduce a circuit consisting of an RC network with a large number of independent current sources while maintaining the same level of node voltages in the reduced circuit as corresponding node voltages of the circuit before the reduction and which has a high reduction ratio.